Investigation of the spirolide profile of Adriatic Alexandrium ostenfeldii by liquid chromatography tandem mass spectrometry

The toxin profile of cultures of Alexandrium ostenfeldii collected along the North-western Adriatic coasts of Italy in November 2003 was determined by LC-MS/MS. The chromatographic separation was carried out by using a reversed phase column and a buffered mobile phase, as suggested by Quilliam et al. for the analysis of various lipophilic toxins . MS detection was accomplished either by using a heated-ESI-linear ion trap-MS instrument, operating in Data Dependent (DD) scanning mode, or a ESI-triple quadrupole MS instrument, operating in full scan MS and MS/MS modes. The spirolide profile of the Adriatic strain was dominated by the recently reported 13,19-didesmethyl spirolide C whose identity was assessed by the presence of three characteristic ion clusters in the LC-MS/MS spectrum of the [M+H]+ ion at m/z 678.5. The Adriatic strain was shown also to produce 13-desmethyl spirolide C, but unlike most of the worldwide strains of the dinoflagellate in which it accounts for >90% of the total spirolide content, this wasn’t the major component. Furthermore, a new spirolide was also isolated in remarkable amounts and its structure assigned to the novel 27-hydroxy-13,19-didesmethyl spirolide C by combined use of LC-MS/MS and NMR evidence. The occurrence of a number of potentially new spirolides was also highlighted and LC-MS/MS-based structural hypotheses are provided for most of them.